Conventionally, positioners have been used in controlling the driving of valves and in controlling the driving of process automation and other common industrial equipment, enabling the control of the degree of opening of a valve through attaching the positioner to the valve.
FIG. 20 illustrates the structure of the critical portions of a positioner that enables the control of the degree of opening of a valve. In this diagram, 100 is a positioner, where this positioner 100 is structured from an electro-pneumatic converting portion 101 for converting to a pneumatic signal Pn a valve opening signal that is sent in an electric signal from a higher-level controller 200, and a pilot relay (pressure signal amplifying device) 102 for amplifying the air pressure signal (input air pressure) Pn, converted by this electro-pneumatic converting portion 101, and outputting it to a valve 300 as an output air pressure signal (output air pressure) Po.
The pilot relay 102 used in such a positioner 100 may be of the single-action type, wherein a single output air pressure Po is outputted for a single input air pressure Pn, or a double-action type, wherein two output air pressures Po1 and P-o2 are outputted in relation to a single input pressure Pn. The double-action pilot relay 102 has two output ports, where the output air pressure Po1 of the first output port is higher than the output air pressure Po2 of the second output port when the valve 300 is operated in the forward direction, and the output air pressure Po2 of the second port is higher than the output air pressure Po1 of the first port when operated in the reverse direction.
FIG. 21 illustrates a structure of a single-action pilot relay. In this figure, 401 is a housing, where an input air pressure chamber 402, a supply air pressure chamber 403, an output air pressure chamber 404, and a discharge air chamber 405 are provided within the housing 401. Moreover, a diaphragm 406 that is displaced by the input air pressure (the nozzle back pressure) Pn that is directed into the input air pressure chamber 402 is provided within the housing 401, where a valve driving member (a movable body) 407 is provided on the diaphragm 406 so as to be able to move in the direction of the arrow A and the direction of the arrow B. The valve driving member 407 has an opening 407a located at the output air pressure chamber 404, and a discharge air duct 407b that connects the opening 407a to the discharge air chamber 405. Moreover, the output air pressure chamber 404 and the discharge air chamber 405 are separated by a diaphragm 408, where this diaphragm 408 is provided between the housing 401 and the valve driving member 407.
A dividing wall 409 is provided between the supply air pressure chamber 403 and the output air pressure chamber 404. A connecting hole 409a, for connecting between the supply air pressure chamber 403 and the output air pressure chamber 404, is formed in this dividing wall 409. Moreover, a poppet valve 410, that can move to the left and the right, is provided through this connecting hole 409a. The poppet valve 410 has, integrally, a discharge air valve 410a for opening and closing the opening 407a of the valve driving member 407, and a supply air valve 410b for opening and closing the connecting hole 409a of the dividing wall 409. Moreover, the output air pressure chamber 404 is provided with a spring 411 for biasing the poppet valve 410 in the direction of the arrow B, that is, in the direction wherein the supply air valve 410b closes the connecting hole 409a. 
In this pilot relay supply air pressure Ps is supplied through an air supplying pipe 412 to the supply air pressure chamber 403, and the input air pressure Pn is directed to the input air pressure chamber 402 through a nozzle back pressure injecting pipe 413. Moreover, the output air pressure Po is outputted to the valve 300 from the output air pressure chamber 404 through an air outputting pipe 414. Note that the discharge air chamber 405 is connected to atmosphere.
In this pilot relay, when the input air pressure Pn is increased, the diaphragms 406 and 408 move to the side of the arrow A, and, concomitantly, the valve driving member 407 that is supported on the diaphragms 406 and 408 moves to the side of the arrow A. As a result, the valve driving member 407, in accordance with this movement, pushes the poppet valve 410 downward against the biasing force of the spring 411, and, accordingly, the supply air valve 410b of the poppet valve 410 opens the connecting hole 409a. At this time, the opening 407a of the valve driving member 407 is closed by the discharge air valve 410a of the poppet valve 410.
As a result, the air that is supplied to the supply air pressure chamber 403 through the air supplying pipe 412 is introduced into the output air pressure chamber 404 through the connecting hole 409a, to be supplied to the valve 300 through the air outputting pipe 414.
On the other hand, when the input air pressure Pn is decreased, the diaphragms 406 and 408 move to the side of the arrow B, and, concomitantly, the valve driving member 407 that is supported on the diaphragms 406 and 408 moves to the side of the arrow B. At this point, the poppet valve 410 is pushed upward by the biasing force of the spring 411, and, accordingly, the supply air valve 410b of the poppet valve 410 closes the connecting hole 409a. At this time, the opening 407a of the valve driving member 407 is opened by the discharge air valve 410a of the poppet valve 410. As a result, the air within the output air pressure chamber 404 enters into the discharge air duct 407b through the opening 407a of the valve driving member 407, to be discharged to the discharge air chamber 405.
In this way, the valve driving member 407 and the poppet valve 410 are actuated by the input air pressure Pn that is directed into the input air pressure chamber 402, where the action thereof causes the amplified output air pressure Po to be outputted to the valve 300 through the air outputting pipe 414. In this case, the output air pressure Po can be adjusted through adjusting the pressure of the input air pressure Pn.
In this pilot relay, the input pressure is expressed by An×Pn, the product of the input air pressure Pn and the effective surface area An of the diaphragm (the input diaphragm) 406, and the output pressure is expressed as Ao×Po, the product of the output air pressure Po and the effective surface area Ao of the diaphragm (the output diaphragm) 408.
When the input pressure An×Pn is in equilibrium with the output pressure Ao×Po, then the supply air valve 410b is seated in the connecting hole 409a of the dividing wall 409, and, at the same time, the discharge air valve 410a is seated in the opening 407a of the valve driving member 407, and both the supply air and the discharge air is stopped. That is, when the input pressure and the output pressure are in equilibrium, the equation of An×Pn==Ao×Po is satisfied.
In this pilot relay, the ratio of the output air pressure Po to the input air pressure Pn is defined as the gain G (CG=Po/Pn). Because the equation An×Pn=Ao×Po is satisfied, this gain G is Po/Pn=An/Ao, so the gain C can be expressed as C=An/Ao. The higher this gain G, the higher the output air pressure Po, depending on the input air pressure Pn, making it possible to increase the responsiveness of a positioner. Given this, in order to achieve an increase in gain in the pilot relay, either the effective surface area An that bears the input air pressure Pn must be increased, or the effective surface area Ao that bears the output air pressure Po must be decreased.
In this case, when the effective surface area An that bears the input air pressure Pn is increased, this leads to a decrease in responsiveness. Moreover, this is undesirable because it leads to an increase in the size of the pilot relay area. Because of this, rather than increasing the effective surface area An that bears the input air pressure Pn, preferably the effective surface area Ao that bears the output air pressure Po is decreased.
Moreover, in this pilot relay, a force that is determined by the difference between the supply air pressure Ps and the output air pressure Po, and by the diameter of the supply air port, acts on the supply air valve 410b of the poppet valve 410, given the structure thereof. This acting force is because of a dead band wherein there is no switching between supplying air and discharging air in relation to a change in the input air pressure Pn (See, for example, Japanese Unexamined Patent Application Publication 2001-75651 (“JP '651”) (Paragraphs 0021 through 0023)).
Given this, in order to ameliorate the non-linear properties of the supplying air and discharging air due to the dead band, in the pilot relay set forth in JP '651 a relatively large-diameter bleed hole is provided, so that the output air pressure can escape to atmosphere. Moreover, in the pilot relay set forth in Japanese Unexamined Patent Application Publication 2004-360805 (“JP '805”), a bleed hole with a relatively large diameter is provided so that the supply air pressure is introduced into the output air pressure chamber, to escape to atmosphere.
However, in the pilot relays set forth in JP '651 and JP '805, in order to quickly settle the output air pressure after a discharge operation it is necessary for the bleed rate to be large, and there is a problem in that this increases the steady-state air consumption rate.
The present invention is to solve this problem, and the object thereof is to provide a pilot relay wherein it is possible to increase the speed of settling of the output air pressure, without increasing the bleed rate.